The present disclosure relates generally to a variable refrigerant flow (VRF) system and more particularly to a VRF system that uses extremum-seeking control (ESC) to control the operation thereof. VRF systems may be used in heating or cooling a building Refrigerant can be either heated or cooled within outdoor VRF units and delivered to indoor VRF units within the building The refrigerant can then be returned to the outdoor VRF units to be either heated or cooled again.
ESC is a class of self-optimizing control strategies that can dynamically search for the unknown and/or time-varying inputs of a system for optimizing a certain performance index. ESC can be considered a dynamic realization of gradient searching through the use of dither signals. The gradient of the system output y with respect to the system input u can be obtained by slightly perturbing the system operation and applying a demodulation measure. Optimization of system performance can be obtained by driving the gradient towards zero by using a negative feedback loop in the closed-loop system. ESC is a non-model based control strategy, meaning that a model for the controlled system is not necessary for ESC to optimize the system.